Rational Design And Synthesis Of Metal Organic Framework-Based Nanostructures For Electrocatalytic Applications

The global energy and economy demand have risen rapidly due to continuous world population growth.The world environmental pollution and energy crisis owing to excess utilization of traditional fossil fuels become serious global issue.Thus,the energy shortage and environmental pollution calls for urgent solution.Several scientific researches and technologies have been explored including electrocatalysis and photocatalysis to address the above-mentioned problems.However,due to the poor efficiency and low activity,the catalytic materials are still unable to satisfy the required demand and it is significantly critical to develop cost-fair and highperformance catalysts.Metal organic frameworks exhibit unique features like high internal porosity,large surface area and diverse functionality.Therefore,they have been extensively explored in broad application prospects such as catalytic energy conversion and storage,drug delivery,sensing and biomedicine.Even though,progressive works have been made on strategic preparation of MOF-based nanomaterial catalysts,there are still some shortcomings anticipated to improve.Therefore,it is paramount to rationally design and synthesize the MOF-based catalysts to optimize their performance so as to meet the required needs.In this thesis,a variety of synthesis approaches were employed to rationally optimize the morphology,structure and composition of materials and series of works were carried out on MOF-based catalysts for energy conversion applications and the main research findings are as follows:1.MOF-derived W-doped MoP nanospheres electrocatalyst was developed by applying a simple and facile synthesis approach.Particularly,successive hydrothermal method at 120℃ and heat treatments followed by a phosphorization process at 350℃ was followed.The as-fabricated metal phosphides catalyst demonstrated efficient HER catalytic activities in pH universal electrolyte(η10=63,71,and 82 mV in acidic,alkaline and neutral media respectively).Moreover,excellent long-term electrochemical stability and fast interfacial electron transfer kinetics was exhibited from as-prepared material.The superior intrinsic activity is credited to the large surface area acquired from starting MOFs precursor and introduction of W followed by phosphorization.2.Simple and facile preparation strategy was employed to rationally synthesize nanostructured hybrid NiCo2S4/Fe2O3@CC derived from MOFs.The heterostructured hybrid NiCo2S4/Fe2O3@CC materials grown on carbon cloth was fabricated by two consecutive steps.Primarly,MOF grown on carbon cloth was prepared by a simple hydrothermal method using metal salts(Co2+,Fe3+ and Ni2+),1,4-BDC and DMF as precursors.Finally,the isolated MOF(NiCoFe MOF/CC)material was treated with 500 mg of sublimed sulfur powder at 350℃ under nitrogen flow to obtain NiCo2S4/Fe2O3@CC.The as-synthesized hybrid nanomaterial was applied as electrocatalyst toward oxygen evolution reaction(OER).High porosity,abundant active sites and hybrid heterostructure together with unique architectures merited the as-developed hybrid NiCo2S4/Fe2O3@CC for exhibiting excellent intrinsic activities with 190 mV overpotential at 10 mA cm-2.Additionally,the as-fabricated nanohybrid exhibited remarkable long-term stability.3.Three-dimensional hybrid heterostructures with abundant active sites induced by W-doping was rationally designed.The 3D hybrid heterostructured material(WNiS2/MoO2@CC)was synthesized via facile hydrothermal method followed by sulfurization using MOFs as precursors.In the primary procedure,NiMo-MOF@CC was firstly prepared using hydrothermal process.Secondly,W was hydrothermally doped into NiMo-MOF@CC precursor followed by thermal annealing with sublimed sulfur at 400℃ for 2 h in the H2/Ar(5%/95%)atmosphere.The as-prepared material was applied as a bifunctional electrocatalyst toward UOR and HER.Attributable to the combined merits of 3D porous structure,abundant accessible active sites,conductive carbon cloth support and the heterojunction of MoO2 and NiS2,the asdesigned WNiS2/MoO2@CC exhibited superior UOR(1.3 V@10 mA cm-2)and HER(η10=52 mV)catalytic activities.Meanwhile,the urea electrolytic cell(HER‖UOR)performance of material showed excellent catalytic activity with low required cell voltage(1.372 V@10 mA cm-2),shows much better efficiency than conventional water electrolysis.In the meantime,the catalyst exhibited remarkable long-term electrochemical stability of 24 h with insignificant loss of current density.4.Finally,MOF-derived nanostructured(FeNiCoCrCu)3O4 high entropy oxides electrocatalytic material was designed using hydrothermal synthesis approach followed by high temperature treatment.In this work,first HE-MOF was synthesized using hydrothermal synthesis approach 120℃ and the high entropy oxides(HEOs)were prepared by high temperature annealing(800℃)of high entropy metal organic framework(HE-MOFs)in air atmosphere.Active site rich single crystalline phase HEOs with abundant oxygen vacancies was produced.The as-designed material exhibited excellent UOR(1.35 V@10 mA cm-2)and OER(η10=270 mV)catalytic activities.The outstanding catalytic performance is credited to the starting MOF precursor by providing,active site rich large surface area;additionally,the favorable high-entropy effect has substantial catalytic contribution.